Electric heating furnace



NOV. 25, 193. R' E TALLEY 1,783,155

ELECTRIC HEATING FURNACE Filed June 2, 1927 5 Sheets-Sheet l Nw. 25, 1930. E, TML@ L73155 ELECTRI C HEATI NG FURNACE Filed June 2, 1927.

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.1Nov. 25, 1930. R. E. TALLEY 1,783,155

ELECTRIC HEATING FURNACE.

Filed Jure 2, 1927 5 sheets-neet 5 1 A" -LJ ll INVENTOR Nov. 25, 1930.

R. E. TALLEY ELECTRIC HEATING FURNACE Fileduune 2, 1927 5 sheets-Sheet 45 F" rfs.

N 7 91 91"' 'w v INVENTOR Patented Nov. 25, 193@ UNITED' STATES PATENT OFFICE RANDAL E. TALLEY, OF IRWIN, PENNSYLVANIAJ ASSIGNOR T GEO`RGE J. HAGAN COM- PANY, OF PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA ELECTRIC HEATING FURNACE L Application filed June 2,' 192'?. Serial No. 195,988.

This invention relates to electric heating furnaces, more particularly to heating furnace for industrial use in the heat-treatment of metals;

Electrically operated heating furnaces for heat treating metals are rapidly gainin favor because of the heat regulation aiforde by the use of electric current. In the apphcation of electric furnaces for industrial heating problems, the main essential is to control the heating of the product. The temperature ofcthe heating chamber may be maintained Within close limits but if the heating time is not also accurately controlled, the temperature'of the finished product will not be uniform. It is, therefore, desirable to positively control the heating cycle as Well as the temperature.'

The rotary hearth furnace is designed `with this object in view and with the maintainance of suitable and practically constant furnace temperature, it is a matter of controlling the speed of travel of the hearth through the heating zone to obtain proper heating of the articles treated.

In the initial installations of rotary hearth furnaces, the hearth Was continuously, rotated and in some cases provisions were made for 'varying the speed of rotation to' secure proper timing of the heat cycle. It was found.v however, that the constantly rotating hearth did not always travel at the exact speed for which it was set dueto variations in thefpower line voltage of the drive motor or due to variations in the friction of the vmoving parts and'for other causes.

I have discovered that the disadvantages resulting from variations in the speed of the hearth drive may be overcome by advancinar the hearth intermittently in -predetermined increments. This is successfully accomplished b v the elimination of the human clement, which necessitates the employment of automatic operating mechanism. In addition to the automatic operation for intermittently advancing the hearth, it is desirable to automatically' discharge the heated articles from the furnace to obtain full automatic operation and positive control of the heat cycle.

In accordance with the present invention, I provide automatic regulation for rotary hearth operations and it is among the objects thereof to provide a rotary furnace in which the hearth shall be automatically and intermittently advanced in predetermined increments.

Another object of the invention isto provide a rotary furnace of the above designated character which shall` embody a dump mechanism for automatically discharging the articles heated.

Another object of the invention is to coordinate the operations of the work-discharge or dump mechanism with the hearthadvance mechanism so that the operations of said mechanisms are inter-dependent.

Another object of the invention is to provide mechanism for automatically lifting the charging door, which shall be mechanically interlocked with the hearth drive vand dump mechanism.

Another object of the invention is to provide anelectrical control system by means of which the actuating means for the operating mechanism to carry out the entire sequence of automatic operation' shall be electrically interlocked and which shall permit of manually and severally controlling the individual actions.

AStill another object of the invention is to provide an automatic rotary hearth furnace of the above designated character which shall be of simple and durable mechanical construction Whichshall comprise a minimum number of operating parts and which shall be efficient in its operation for the heat treatment of steel in production quantities with uniform results.

In the accompanying drawings'constituting eis a part hereof and in which like reference characters designate like parts, Fig. 1 is a sectional elevational view of a portion of a rotary furnace structure embodying the principles of my invention; Fig. 2 is a plan view thereof partly in section; Figs. 3, 4 and 5 are tively of the dump drive and door operating mechanism and Fig. 8 is a wiring diagram of a control system employed in the automatic and manual operation of the rotary hearth furnace.

Referring to Figs. 1 and 2 of the drawings the structure therein illustrated com-- prises a pair of circular inner and outer furnace Walls 1 and 2 respectively and top and bottom walls 3 and 4 respectively, the latter being provided With an annular opening in which the rotary hearth generally designated at 5 is operatively disposed. The rotary hearth is mounted upon a bearing support 6 and iS rotated by a drive mechanism generally designated at 7. The rotary hearth bearing member comprises a casting 8 having a ball race 9 and gear teeth 10, the latter being in engagement with a beveled gear 11 mounted on the end of a drive shaft 12 which is rotatably journalled in bearings 13 and 14 of the drive mechanism in the manner illustrated. The drive shaft 12 is geared through a gear train 15 to a gear reduction mechanism 16, Fig. 3, comprising the usual Worm gear reduction, the Worm element of which is secured to or made integral with a shaft 17 which is coupled at 18 to a drive motor 19. The rear mechanism is mounted on a common ase plate 2O which may be disposed in any convenient position underneath the furnace structure.

Referring to Figs. 1 and 2, a plurality of segment-shape Work support trays 22 are supported on the hearth 23 by trunnion members 24 which engage the tray supporting lugs 25. The trays are provided with lugs` 26 which are illustrated as substantially L- shape to provide a suitable supporting base. The trays are adapted for pivotal movement on the trunnion members 24 as shown in dotted lines in Fig. 1 for the purpose of discharging their contents through a chute 27 which directs the Work or charge to a quenching medium or conveyor mechanism (notI shown).

The work supporting trays 22 divide the rotary hearth into a plurality of stop stations corresponding in number to the number of trays on the hearth. By advancing the hearth one station, a tray is brought into alinement with the discharge passage 27 of the furnace and by advancing it another station, the adjacent tray is moved forward to the discharge passage, etc.

The trays are automatically rotated on their trunnion supports by a dump mechanism which is operated through a suitable mechanical linkage to engage the underside of the tray and rotate it on its hinged support to discharge its contents into the chute 27. The tray-engaging mechanism comprises the following elements: a bifurcated lever 3() having a tray engaging lug 31 pivoted at 32 of its arm 33 to a bell crank lever 34 and at 35 of its arm 36 to a link 37. The bell crank lever 34 is pivoted at 38 to a stationary lug 39 and the link 37 is similarly pivoted at 40. An actuating link 41 is pivoted at 42 to crank lever 34 and extends through an opening 43 in the roof of the furnace. The dump actuating linkage functions by lifting the trays on their pivots 24 when the link 41 is lifted by the dump drive mechanism to be hereinafter described.

The arm 30 through its connecting linkage is maintained in a horizontal position during its upward movement to the position shown in dotted lines which is the uppermost raised position of the tray.

The engaging lug 31 at the end of the tray lifting arm moves upward in the arc of a circle about pivot 24 as a centre. There is therefore no relative movement between engaging lug 31 and tray 22 at the point of contact thereby eliminating friction and Wear, both of which are important. Wear on point 31 would change the discharging angularity of the tray in its upward position and friction would put a heavy load on the lifting arm and its mechanism.

As shown in Fig. 2, the furnace chamber is provided with a transverse baffle Wall 45 which is disposed between the discharge chute or passage 27 and the charging passage 46 to prevent the cold air entering the furnace at the charging passage from passing to the heat Zone of the furnace chamber which is at the discharging passage. Cold air is prevented from entering at the discharge passage by sealing the end of the chute which is constantly immersed in the quenching medium for this purpose. The furnace may be provided with-one or more doors 47 which are adapted to close the charging passage and also the discharging passage depending upon whether the latter is in the form of an inclined chute for discharging from a tilted tray or a horizontal passage in line with the surface of the hearth for discharge of the product by means of a pusher or other suitable device.

The doors and dump mechanism are automatically actuated by the following mechanism: Referring to Figs. 6 and 7, the link 41 iwhich is pivotally connected to the hell crank lever 34 of the tray lifting mechanism is shown pivotally connected to a lever 50 which is pivotally supported at by bearing brackets 61 on a frame structure (52 which is mounted above the furnace. The end of the lever 50 is provided with a roller or cam follower 63 which contacts with a cam G4 of the dump drive mechanism. The cam is mounted to rotate with a drive shaft (S5 having a crank 66 at one end thereof and which is driven through a reduction gear (57 that is connected by a gear train G8 to a drive motor 69. The crank 66 is connected h v a link 7() to a crank arm 71 which is mounted on an oscilllO lili) lating rocker shaft 72 supported in bearings as shown in Fig. 7. Connected to the shaft 72 are a pair of levers 73 which are pivotally connected at 74 to chains 75 that operate the furnace doorsV 147. The free en-ds of the ylevers 73 are provided with counterweights 76 which may be adjusted to any suitable position in the usual manner. The shaft 60 of the oscillating lever 50 is also provided with an upwardly projecting crank arm 77 which is connected by a coil spring 78 to a vertical support 79. The coil spring 78 being adjustable for tension by a pair of adjusting nuts 80. The-purpose of the tension spring is to normally bias the lever so that the cam follower 63 exerts pressure against the face of the cam 64. The cam at its high side is provided with a plurality of notches 81 which are adapted to violently agitate the arm 50 and its connected tray lifting link 41 when engaged by the cam follower for the purpose of loosening an material which may have a tendency to a here to the tray 22 when the latter is at or near its lifted position.

As shown in Fig. 7 the vertically movable tray lifting link 41 is provided with a switch contact 82 which is disposed in the path of a stationary contact 83 and with the latter constitutes a switch element which functions in a manner to be hereinafter explained.

The rotary hearth drive and the dump drive and door operating mechanisms are controlled by a time clock of a well known type, through a pluralityof rotary switches which are illustrated in Figs. 4 and 5 and which are desi nated at A, B and C in Figs. 3 and 6 of the dTrawings. The switch mechanism -comprises a housing 85 in which isrotatably journalled a reduction gear mechanism 86, the driven shaft of which operates a drum 87 on which are mounted a contact bar 88, Fig. 4. The drums are rotated at a speed determine-d by the ratio of the gears 86 and the gear ratio of theconnecting gear Wheels 89 which as shown in Fig. 3 are operatively engaged with the gear train 15 of the hearth drive 7 or as shown in Fig. 6 with the dump drive mechanism. Mounted in` the housing 85 is a stationary contact element comprising contact lingers 90 and 91 constituting terminals for line connections 92 of the control or operating circuit. As is clearly illustrated in Fig. 5, the lingers 90 and 91 are in spaced relation and arranged to successively contact with the bar 88 of the rotating drum, this being for a purpose to be hereinafter stated.

Before disclosing the voperation 'of the mechanism it is well to review the objects to be accomplished and Aas previously stated. these are as follows: to rotate the hearth a fraction of a revolution corresponding to the spacing of the dump trays; to lift the charging door to admit a new charge to -any empty tray; and to accomplish these functions in In addition to the interlocking eiiect of the rotary switches A, B and C, a relay having onenormally closed contact and two normally open contacts are employed in the dump drive and hearth drive circuits, the relays being respectively designated at 138L and 3a. As shown in Fig. 8, the rotary switch C has two contact fingers 90 and 91 whereas the rotary switches A and Bare provided with lingers 90, 91." and 92 and 90"'. 91 and 92" respectively. The fingers of the respective rot'ary switches A, B and C make momen:

tary contact with their armature bars 88', 88" and 88 which is the bar designated at 88 in Fig. 4 of the drawings. The lingers 90', 91" and 92 of the switch B will make continuous contact with their common armature.

bar 88 when the hearth is in the correct position for the tray 22 to be lifted or for the dump mechanism to proceed. The switch C has its fingers 90 and 91 in contact with its armature bar 88 when the dump drive is in the correct` position for the hearth to proceed, that is, when the tray is rest-ing on the hearth. The finger 91 however makes a momentary contact with the bar 88 and accomplishes a momentary connection with finger 90 for reasons hereinafter stated.

There are two signal relays, 9a and 19 of the normally open contact type. In addition there is a. time clock 2a having a contact 14a and there are two push button stations 1 and 2 designated at 8a and 17a respectively, also a push button station switch at 5.

When the power line 101 and 102 is ener gized by amaster switch (not shown), rated voltage is applied to the system and the time clock motor 2, M starts `running and after a definite interval of time closes the time clock contact 14a which constitutes the starting signal. The current path is to the left of main 102, down branch 102', through the contact 81 of the limit switch which is connected to the dump actuating link 41 as shown in Fig. 7 of the drawings, the contact being closed when the dump tray is in Y its seated position on the hearth. The current flows through the limit switch to the right on line 104; down past the hearth drive contactor coil 6a, back to the left on line 104.

down to the time clock contact 14a. through it to line 108 through the normally closed contact 8a of push button station 1 to line 107, through the resistance 7 a the hearth drive relay coil 1L1 thence upward to main 101.

Current in the hearth drive relay causes it to pull its armature down and close the normally open contact between lines 107 and 114 and between lines 101 and 106 and open .the normally closed contact between the lines 103 and 104.

Current now gaining access to line 114 as before is carried through the hearth drive contactor coil 6a to line 106, also through the closed contact of the hearth drive relay to line 101 up branch 101 to main 101. This causes the hearth drive contactor to close and start the hearth drive motor. Part of the current in line 114 passes to the right under the hearth drive contactor coil 6a through the hearth drive relay up contacts 3 to line 107, down and to the through resistance 7 a and hearth drive relay coil 1 to branch 101 and up to main 101. This is the retaining current path and-by means of it the hearth drive relay 3 is he'ld closed after the time clock contact 14a is broken.

After the normally closed contacts lines 104 to 103 are open, it is impossible to get a current path through the dump drive relay coil 23a so that it is impossible to start the dump drive when the hearth drive is runing. With the circuits established, as explained, the hearth drive is in operation. The rotary switches A and B are geared into the hearth drive mechanism by their connections with the gcar train 15 in such a manner that the rotary switches make one revolution and one contact, the rotary switch A is set ahead of rotary switch B about degrees and will make contact first and pass oli' so that switch B when making contact next stops in the made position.

When the rotary switch A makes contact and passes by, the following current paths are open :from main 102 to line 14 as before mentioned, through the closed contact to line 7 down between the resistance 7'1 and contact 8a of push button station 1 to the signal relay coil 11 through the coil to line 111, down through resistance A to line 101 to branch 101 to main 101. Current in the signal relay coil 11a closes contacts 109 to 110 and 101 to 111. Retaining current then flows from line 114 across hearth drive relay at the right to to branch 101 103 to 107 down through signal relay coil 11 to 111, up through 111 and through signal relay contact 9 to line 101 and out to main 101. The retaining current holds the signal relay closed as long as the hearth drive relay 3a remains closed. 1n closing the connection 109 to 110, the first step accomplished is shorting the hearth drive relay coil 1R. This shorting is accomplished by rotary switch B.

In making contact of the rotary switch A,

left thence to the right the dump drive circuit is partly established in the following manner z-The current passes from main 102 and branch 101 through limit switch 81 to 1 line 113 to the right through signal relay coil 21a to line 121 and push button station switch 5a to and through line 105 through rotary switch left to line 101 and to main 101. Current in the signal relay coil 21a closes contacts 119 to 117 and 121 to 101 of the signal relay 19. Retaining current then flows from main 102 through rotary switch up through line 113,

signal relay coil 21, and line 121 through signal relay contacts 19a to line 101 and to main 101. 119 and 117 constituting the partialsignal circuit to the dump drive.

When the rotary switch B subsequently makes contact the E. M. F. formerly impressed across the hearth drive relay coil 109 to 101 becomes active through the circuit consisting of line 109, signal relay contacts 9, 109 to 110 line 110 to rotary switch B branch 101 to main 101. Short circuiting the hearth drive relay coil 1 in this manner, causes it to drop its armature and de-energize the hearth drive contactor coil 6*. The hearth motor stops and as the load kis heavy, there is no 'appreciable drift and rotary switch B stops in the continuous make position. This constitutes a signal to the dump drive motor through the following circuit: main 101, branch 101', rotary switch B, line 103 through the normally closed down contacts of the hearth drive relay 3 to line 104 to the left and down 104 to the knife switch 5a to the left on line 117 through the signal relay contacts 19n to line 119, up line 119 and to the left through resistance 23b and dump drive relay coil 23El to branch 102 to main 102.

The dump drive relay 13L closes, opening the contact 113 to 114 and making it impossible to start the hearth drive even it the closed circuit 14L should make. Contact to 116 is made, energizing the dump drive contactor coil 168L and starting the dump motor. Contact 117 to 119 feeds retaining current through the dump drive relay coil 23, rotary switch C is driven open and signal relay coil 21a, 113 to 121 is released. The drive continues running until switch C makes contact 90 to 91 shorting the dump drive relay coil 23 and stopping the drive as the limit switch 81 drifts into contact which is at the time the dump tray 22 assumes a normal position on the rotary hearth. The mechanism now stands ready for the next clock signal. This completes the full automatic operation of the entire system and the next signal given by the clock will cause the entire sequence of `operations to be repeated in the order mentioned.

The charging doors 47 by virtue of their connection through levers 73 with the dump llO Lasarte drive mechanism are automatically opera-ted at timed intervals, to permit charging the trays after they are dumped.

lf it is desired to make the primary signal manually, this is accomplished by using push button station switch 1 which in its normal closed position as shown, is an essential factor in the closed current path through the time clock-contact 14a when that contact is made. 1n this position, push button has its arrow pointing to the left and when depressed in this position and turned 90 degrees to the right, no signal will be given even though the time clock motor 2a is running and the time clock contact 14a is making. The push button may be turned 90 degrees further to the right and left on open circuit, or from this new position it may be depressed until contact is made between lines 107 and 114 from which the push button 8a will spring back to the normal open position. llt will be seen that contact 114 to 107 constitutes a signal to the hearth drive relay coil as the time clock control 14 has been by-passed or short-circuited. By this means the man ual control of the entire sequence of events heretofore described as automatic, has been accomplished.

If it is desired to operate the hearth drive alone automatically, the knife switch 5a is opened and the push button 8f" is in the normally closed position. The dump drive, being in the correct position, permits the clock contact 14a to energize the hearth drive relay coil 1a and start the hearth drive, but as the knife switch 52L is open, rotary switch A cannot energize signal relay coil 21, 113 to 121, and even though the hearth drive stop in the correct position for the dump drive to proceed, the dump drive relay coil 23a obtains no signal to start nor can the dump drivey contacter coil 16 receive current if the signal relay armature 19EL is actually closed by hand. Forthe manual operation of the dump drive alone push button station 17 a is employed. rlhis is a single button push button of the momentary contact type and its function is as follows: The time clock 2a is disconnected by depressing ush button 8'l and turning it 90 degrees to t e right. rlhis obviates any chance of a clock signal. rlhe knife switch 5a is then closed to establish a current path therethrough from rotary switch B and main 101. rlhe hearth drive must of course be in the correct position for the dump drive to proceed. Push button 1'(a by-passes the signal relay 19a, the coil 21a of which is between 113 and 121 and cannot be energized because rotary switch A is on open circuit. By closing push button 17a, dump drive relay coil 23a is energized and closes its armature thereby setting up a retaining current path and starting the dump drive. Shorting of the dump drive relay coil 23a by rotary switch C is accomplished as before and the drive is i brought to rest at the completion of its cycle without the possibility of a signal being given to the hearth drive.

If push button 8a is closed inwardly between 114 and 107, starting of the hearth drive will be accomplished manually.' lf `the dump drive is in such position that this contact should not have been made, there will be no signal because the current path of this signal is through the closed contacts of rotary switch C and if the dump drive is not in the correct position for the hearth drive to proceed, the contact 113 to 102 will not be made, hence no daniage'can be done by using push button 8 when it should not have been used.

In a very similar manner push button 1'?a is effective only when the knife switch 5a is closed and even then there can be no signal given to the dump drive relay coil 23Pl unless the hearth drive is correctly located.

It is evident from the foregoing description of this invention that the rotary hearth dump drive furnace illustrated and described thereinl may be automatically or manually controlled to advance the work supported on the trays of the hearth intermittently through the furnace chamber, sto p the hearth in its proper position in line with the discharge passage of the furnace, operate the dump mechanism to discharge the work from the furnace and open the charging doors to permit the entering of the new charge into the empty tray and then automatically proceed to the next charging and discharging station whereby the heating cycle 'of the article to be treated is positively controlled which is the object herein desired to accomplish.

Although one of the embodiments of my icc l' invention has been herein set forth and described, it will be obvious to those skilled in the art that various modications may be made in the details of construction and in the arrangement of the several cooperating parts without departing from the principles herein set forth.

I claim:

1. A heatin furnace comprising in com bination, a furnace chamber, a movable hearth, a plurality of work supports mounted on said hearth, a drive mechanism for advancing said hearth through the furnace chamber, a dump mechanism for actuating said work supports to discharge the work therefrom and means for rendering said hearth drive mechanism inoperative during the operation of said dump mechanism.

2. A heating furnace comprising in combination, a furnace chamber, a movable hearth, a plurality of work supports mounted on said hearth, a drive mechanism for advancing said hearth through the furnace chamber, a dump mechanism for actuating said work supports to discharge the work therefrom, means for rendering said hearth drive mechanism inoperative during the operation of sald dump mechanism, and means for rendering said dump actuating mechanism inoperative during the operation of said hearth drive mecha- 1'11Sm.

3. A heating furnace comprising in combination, a furnace chamber, a movable hearth, a plurality of work supports mounted on said hearth, a drive mechanism for advancing said hearth through the furnace chamber, a dump mechanism for actuating said work supports to discharge the work therefrom, and means for co-ordinating the operations of said hearth drive and dump actuating mechanism to render them successively and intermittently operative.

4. A heating furnace comprising in combination a furnace chamber, a movable hearth, a plurality of work supports mounted on said hearth, a drive mechanism for advancing said hearth through the furnace chamber, a dump mechanism for actuating said work supports to discharge the work therefrom, and control means for co-ordinating the operations of said hearth drive and dump actuating mechanism to render them successively and intermittently operative in accordance with a predetermined time cycle.

5. A heating furnace comprising in combination, a furnace chamber, having one or Inore charging doors and a discharge opening therein, a movable hearth, a plurality of work supports mounted on said hearth, a drive mechanism for advancing said hearth through the furnace chamber, a dump mechanism for actuating said work supports to discharge the work through the discharge opening of the furnace, and mechanism for opening said charging doors, said hearth drive, dump, and door operating mechanism being automatically actuated, to retain the work for a predetermined period of time in the furnace chamber, and to automatically discharge the same therefrom at the expiration of such period.

6. A furnace provided with a discharge opening, a rotary hearth within the furnace,

'material carrying panspupon said hearth,

means for rotating the hearth, means operated by the rotation of the hearth for stopping said rotating means as each pan registers with the discharge opening and means operated by the hearth for dumping the pan which re 'sters with the discharge opening.

7. A urnace, a material carrying pan within the furnace, means for moving the pan through the furnace, means for stopping the pan at a predetermined point and means operated by the stopping of the pan for dumping the pan at said point.

8. A furnace, a material carrying pan within the furnace, means for moving the pan through the furnace, means controlled by the movement of the pan for stopping the pan at a predetermined point, and means for dumping the pan at said point.

9. In a furnace, the combination with an annular hearth, means for effecting movement of said hearth, and a plurality of trays pivotally mounted on said hearth, and means controlled by said hearth for effecting a tilting movement of said trays in sequence.

l0. A furnace provided with a discharge opening, a rotary hearth within the furnace, material carrying pans upon said hearth, means for rotating the hearth, means operated by the rotation of the hearth for stopping said rotating means as each pan registers with the discharge opening, means operated by the stopping of the hearth for dumping the pan which registers with the discharge opening and a time element device for restarting the rotating means.

11. A furnace provided with a discharge opening, a rotary hearth within the furnace, material carrying ,pans upon said hearth, means for rotating the hearth, means operated by the rotation of the hearth for stopping said rotating means as each pan registers with the discharge opening, means operated by the stopping of the hearth for dumping the pan which registers with the discharge opening and means for controlling the starting of the rotating means.

12. In a furnace the combination with a pivotally mounted hearth and means for tilting said hearth, of cam actuated means for causing a jarring of the hearth during the tiltingl action.

13. A heating furnace comprising in combination, a furnace chamber, a movable hearth, a plurality of Work supports mounted on said hearth, operating mechanism for advancing said hearth, and for discharging the work from said supports, and a time clock mechanism associated with said operating mechanism to render the latter operative at predetermined intervals of time.

14.. A heating furnace comprising in combination, a furnace chamber, a movable hearth, a plurality of work supports mounted on said hearth, a motor operated drive mechanism for advancing said hearth in the furnace chamber, a motor operated dump mechanism for discharging the work from said work supports, and rotary switches adapted to be actuated by said hearth and `dump drives and electrically connected to the hearth and dump drive motors, said switches being adapted to automatically interrupt the hearth and dump drive motor circuits at predetermined intervals.

15. A heating furnace comprising in combination, a furnace chamber, a movable hearth, a plurality of work supports mounted on said hearth, a motor operated drive mechanism for advancing said hearth in the furnace chamber, a motor operated dump mechanism for discharging the work from said work supports, and rotary switches adapted to be actuated by said hearth and dump drives and electrically connected to the hearth and dump drive motors, said switches being adapted to automatically interrupt the hearth and dump drive motor circuits at predetermined intervals, and a time clock mechanism electrically connected to said rotary switches and drive motor circuits to cont-rol their respective operations by prede v termined time signals.

In testimony whereof, I have hereunto set my hand.

RANDAL E. TALLEY. 

